Minimizing weathering loss by propanepentane priming of gasoline



Nov. 21, 1961 Filed Dec. 15, 1959 VAPOR TEMPERATURE F.

J. M. JORDAN ET AL 3,009,789 MINIMIZING WEATHERING LOSS BYPROPANE-PENTANE PRIMING OF GASOLINE 2 Sheets-Sheet 1 FIGURE! VAPORTEMPERATURE EVAPORATION CURVES FOR GASOLINES OF ".6 TO I2.0 VLTR llOJohn M. Jordon By w 0 7 W Patent Artorney Nov. 21, 1961 LIQUIDTEMPERATURE, "F.

MINIMIZING WEATHERING LOSS BY PROPANEPENTANE Filed Dec. 15, 1959 J. M.JORDAN ET AL 3,009,789

PRIMING OF GASOLINE 2 Sheets-Sheet 2 FIGURE-2 LIQUIDTEMPERATURE-EVAPORATION CURVES FOR GASOLINES OF .6 TO |2.0 VLTR llO 0 5IO I5 20 25 "l. EVAPORATED Charles E. Hemminger John M. Jordan InventorsPatent Attorney United States Patent 3,009,789 MINIMIZING WEATHERINGLOSS BY PROPANE- PENTANE PRIMING 0F GASOLINE John M. Jordan, Plainfield,and Charles E. Hemminger,

Westfield, N.J., assignors to Esso Research and Engineering Company, acorporation of Delaware Filed Dec. 15, 1959, Ser. No. 859,727 5 Claims.(Cl. 44--52) The present invention relates to gasoline fuel compositionsof balanced volatility primed with propane and pentane.

Gasoline is a complex mixture of hydrocarbons which should provide quickstarting automobile engine performance in all types of weather andtemperature conditions. A gasoline with ideal front end volatilitycharacteristics would maximize starting ability, initial warmup andlight end component utilization, but minimize vapor losses and vaporlock. In commercially preparing a gasoline of predetermined volatilityso as to satisfy the conflicting requirements of ideal front endvolatility, the highly volatile butane and some bu-tene fractions frommodern refinery operations are blended as primers with the hydrocarbonbase stock.

The content of butanes in gasoline generally varies from between about4% to about 20% depending upon the season during which the gasoline isto be used. Summer grade gasolines intended for use and storage duringwarm weather should be of the lowest volatility having a Reid vaporpressure of about 7 to 11 psi. and a C, content of 510%. Spring gradefuels are more volatile, having a Reid vapor pressure of 1 0 to 12p.s.i; and containing about 8-12% C hydrocarbons,-while Winter gasolineswhich are the mostvolatileshave a Reid vapor pressure 3,009,789 PatentedNov. 21, 1961 point represents the most suitable value of startingability of 12 to 15 pis.i. and a C, content 'of about 10-18%', The

use of the C -C5 hydrocarbon refinery cut generally referred tohereafter as butane as a priming agent has in herent disadvantagesqinregard to volatility characteristics, and does not lend itself to thebest resolving of the ideal front end volatility requirements ofgasoline.

It is amongthe objects of this present invention to providea methodwhereby a critical mixture of propane and pentane'in gasoline will givebetter front end volatility characteristics than the use of a gasolineconventionally primed with butane alone or butanes and pentanes. It isfurther an object of this invention to set forth a method whereby theaddition of propane-pentane mixtures to debutanized gasoline willmaximize starting ability, initial warm-up and light end component.utilization, and, in particular, minimize vapor and weathering losswhile maintaining a constant vapor lock tendency rating (VLTR) in thegasoline. Further objects of this invention, as well as the natureandscope of this invention will become more apparent from the subsequentdescription.

' As herein defined the startingaability refers to that period of timebetween starting to'turn the engine over and the time when the engine isoperating under its own power. Starting ability is associated with thetemperature point in degrees Fahrenheit at which about 20% of the fuelby volume (or 15% by weight) evaporates. Thus, for example, a fuel whichhas a 20% evaporated point of 125 F.'will give better initial startingability than a fuel whose 20% point is 135 F. With the choke of anautomobile closed, an air/fuel ratio of about 3/1 by weight is suppliedduring cranking. Since an air/fuel weight ratio for typical fuels. Thus,the 20 vol. percent point on a vapor temperature basis as an indicationof starting ability is now seen to be based upon technicalconsiderations and is not an arbitrary figure.

Warm-up refers to that period of time between the time when the engineis operating under its own power to the time in which smooth performance(no hesitation on acceleration) is obtained. Soon after start-up, theoperation may be very rough since the car is so cold that only a smallportion of the fuel is vaporizing. As time progresses and the enginewarms up, the vaporization approaches Thus, high front-end volatility ismost important during the initial rough period of warm-up (initialwarm-up) which usually lasts the first 3-5 minutes after cold start-up,although high mid-fill and back-- end volatility become increasinglyimportant thereafter. Initial Warm-up is probably best associated withthe 158 F. point of the fuel or, to the percentage evaporation by volumeat a fuel vapor temperature of 158 F. Thus, a gasoline with a 158 F.point of 25% evaporation will give better initial warm-up than a fuel of20% evaporation at 158 F.

Although fuels can be blended to give good initial startup and warm-upby increasing the volatility characteristics of the fuel, increasedvolatility increases vapor locking tendencies and the vapor orweathering losses of the fuel. The vapor locking tendencies of the fuelscan be predicted and expressed by the vapor lock tendency rating (VLTR)which utilizes the Reid vapor pressure (RVP) of the fuel and the 158 -F.point of the fuel. The VLTR can be expressed as follows:

VLTR-=RVP+0.13 (percent evaporated at a vapor temperature of 158 F.)

It has been found that fuels possessing equal VLTR values give equalprotection from vapor lock. Vapor lock incidence at a given temperatureincreases with increasing fuel VLTR.

Vapor loss or weathering loss is here defined as the total amount offuel loss from the refinery to the point of utilization intheautomobile. As is apparent, the higher the volatility, the greater thevapor or weathering loss that can be expected. Relative vapor lossesdepend upon the liquid temperature in degrees Fahrenheit necessary toevaporate 2 to 4% of the gasoline, or the relative true vapor pressureat any percentage evaporated in this loss range. This is the typicalloss range between the refinery and car engine. Thus, higher liquidtemperatures for a given percentage evaporated or lower vapor pressuresresuit in lower evaporation losses. The liquid temperatureevaporationloss concept becomes absolute rather than relative, for systems such ascarburetor losses in which actual fuel boiling occurs, rather than airevaporation. In such cases, the liquid temperature in conjunction withthe ASTM distillation data can be utilized to predict the actualpercentage loss. In summary then, higher front end volatility of fuelgives better initial start-up and warm-up, but increases vapor losses orweathering losses and the vapor locking tendency of the fuel.

The hydrocarbon base stock to which the priming agent is added isnormally a blend of a variety of individual stocks, notably pentanes ora C -C out including both parafiins and olefins; light virgin naphtha;depentanized and under cut catalytic naphtha; depentanized and under cutreformed naphtha; depentanized 400 F. end point reformed naphtha;depentanized 400 F. end point thermally cracked naphtha from gas oil andreduced crude; catalytically cracked heavy naphtha boiling between about300 and 420 F.; thermally cracked heavy naphtha; hydroformed naphtha;alkylate obtained by reacting a C -C olefin with an isoparaffin such asisobu-tane; and polymer gas obtained by thermal or catalyticpolymerization of propylene, butenes, and pentenes and mixtures thereof.The blending of these components with light ends including propanes,butanes, and pentanesto meet the aforementioned specifications of thevarious types of gasoline is a well known art. Thus, butanes are used tocontrol Reid vapor pressure, pentanes and light virgin naphtha tocontrol front end volatility, while the volatility and octane level ofthe total available gasoline pool is usually controlled by the severityof the reforming operation so as to produce a balanced pool meeting theaforementioned specifications. The specifications of course vary withthe seasons, While the present discovery is applicable to all grades ofgasoline, it is particularly valuable and its efiect is particularlyadvantageous in connection with the more volatile winter grade typegasolines,

The solution to the problem of how to maximize the starting ability,initial warm-up, and light end component utilization, but minimize vaporlosses and vapor lock, forms the basis of the present discovery. It hasbeen discovered that by pressurizing or priming debutanized gasolinewith a mixture of a propane and pentane primer within certain criticallimits of percentage propane depending upon the type and volatilitycharacteristics of the gasoline desired, to a constant VLTR, betterinitial start-up warm-up and lower vapor losses can be obtained, than bypressurizing the same gasoline with a conventional butane primer to thesame VLTR. The term debutanizing is used in a manner to indicate thesubstantial removal of butane and butenes and similar C C hydrocarbons,but would excluded the accidental inclusion of minor amounts of somebutane and butenes with the commercial propanepentane mixture or theminor residual traces of butanebutenes left in the gasoline afterdebutanizing. Whereas the propane cut for refinery blending ispredominantly propane and propene, traces of C and some butanes may also.be present. Pentanes or pen'tenes may be either Wide boiling cutsincluding mostly pentanes, but having several percent of C present inaddition to perhaps up to of high boiling hydrocarbons; or high puritycuts having over 95% of a particular C compound such as isopentanes.

To more. fully understand the results of this invention, attention isdirected to FIGURES 1 and 2 in which FIG- URE 1 illustrates three vaportemperature-evaporation higher percentage evaporated at 158 F. (byextrapolation) for better initial warm-up; the same VLTR, and in FIGURE2, B has a lower vapor and weathering loss as indicated by the highertemperature in the 24% evaporation range. A comparison of curves B and Bwith C and C will now illustrate that the use of a propane-pen: taneblend comprising propane in a certain definite percentage by volume willmaintain most of the volatility benefits of pentane primed fuel, andstill allow less weathering and result in a better gasoline from aquality standpoint. Curve C has a lower vapor or weathering loss thaneither curve A or B as can be seen by the higher liquid temperatures inthe 2 to 4% evaporation range in FIGURE 2. The. better quality gasolineWill be due to the use of the propane primer, since propane has a higheroctane value than either butane or pentane alone. The utilization of apropane primer, besides decreasing the Weathering loss and maintainingvolatility benefits, will generally give gasoline blends of a higherinitial octane number. Further, the utilization of propane as a primingagent is particularly advantageous to the refiners, since its use willpresent economic advantages along with broadening of the availabile basestocks for use in priming gasoline.

The amount of propane used to obtain the all-inclusive front endvolatility advantages in the propane-pentane priming is critical.Propane substitution for pentane must be in the ratio of only 1 vol. ofpropane to 5 to 12 volumes of pentane backed out, preferably a ratio of1/ 8- 10, to maintain a constant VLTR. This substitution will result inthe total composition of the gasoline having about 1 to 4% by vol. ofpropane and up to about 50% by vol. pentane, the ratio of the pentane tothe propane in the final gasoline composition being about 5/1 to 50/1.'I'hus, increasing propane substitution tends to lower the fuel 158" F.point and to raise the fuel 20% vapor temperature. Thus, for a summertype of gasoline, the critical propane substitution point for pentanehas been discovered to be limited to about 2% by vol., since curves andFIGUREZ illustrates three liquid temperature- VLTR of 11.6-12.0containing a butane primer, an isopentane primer and a prop'ane-pentaneprimer. The distillation curves of winter and spring gasoline would bequite similar to FIGURES 1 and 2, but would have lower ordinate vaporand liquid temperatures. Referring now to FIGURES 1 and 2. with a moredetailed description. Curves A and A are the vapor (FIG. 1) and liquid(FIG. 2) distillation curves of a summer gasoline primed with 10% butaneby volume and having a Reid vapor pressure of 10.3. Curves B and B arethe vapor (FIG. 1) and liquid (FIG. 2) distillation curves of a. summerdebutanized gasoline primed with about 26% by volume isopentane andhaving a Reid vapor pressureof 8.2. Curves C and C are the vapor(FIG. 1) and the liquid (FIG. 2) distillation curves of; a debutanizedsummer gasoline primed with about 24% by volume of a propane-.pentanemixture where the propane constitutes about 1.1% by volume of the finalgasoline composition, and which gasoline has a Reid vapor pressure of9.2. These curves are based on actual laboratory experimental data.

A comparison of curves A, A, B, and B will illustrate the practical andeconomical advantage of priming the same fuel with 2025% pentane ratherthan the conventional 410% butane. In comparison to the butane primedgasoline of curves A and A, curve B in FIGURE 1 has a lower 20% vaportemperature for superior starting;

this is about the percentage point at which the 158' F. evaporationpoint for the blend becomes lower or where the 20% vapor temperatureexceeds that of the comparable butane primed gasoline (e.g., from 2 to25 butane). This is the point at which the advantage of thepropanepentane priming of fuel over the butane primed fuel with respectto cold starting and initial warm-up is lost. Even greater advantagesfor propane-pentane primed fuels can evapgrafion curves 3]} for summergasolings art a constant obtained in the winter grade 0f gZiSOlll'lQ. Inthe winter gasoline, higher volatility levels are needed for goodstartup and warm-up and thus, the more volatile butanes must be added tothe pentane normally in the gasoline to reach the desired volatilitylevel. The same problems exist in winter gasolines as previouslydiscussed since higher VLTR levels-up to or even above 19.0 aredesirable. The use of propane-pentane priming of winter fuels has manyadvantages. The higher VLTR requiredcannot be reached with pentanepriming alone since even 50% pentane in the base fuel would only resultin a RVP of about 11 and a 158 F. point of perhaps 55%. This would givea maximum VLTR of 18.2. The use of 1 to 4% by volume propane in a ratioof between 5 to 12 volumes of pentane backed out for each volume ofpropane added with a preferred ratio of 8 to 10 volumes of pentanebacked out to each volume of propane added has been discovered toprovide a. winter grade of gasoline superior in starting ability,initial warm-up and with low vapor loss in comparison to the. samegasoline conventionally primed with butane and pentane. The discoveredcritical amount of propane added to the fuel blend and thus,consequently, the amount of pentane backed. out, will once again bedependent upon the propane-pentane fuel maintaining a lower 20% vaportemperature point and a higher percent evaporated at 158 F. than thebutane-pentane fuel. The propane-pentane fuel in order to have the sameVLTR protection as the butane-pentane fuel will necessarily have a Reidvapor pressure at least as low as the butane-pentane fuel. Furthermore,the propane-pentane primed fuel maintaining all the volatilityadvantages for start-up and warm-up will give better advantages thanbutane-pentane primed fuel in vapor losses, since it will only give highlosses in the unusually low loss region of less than 1 evaporation. Evenbefore this minor amount is evaporated, the true vapor pressure will belower for the propane-pentane gasoline and, thus, the vapor loss ratewill continue to be less thereafter.

The practical value of the present invention in regards to vapor lossprotection can be further illustrated by the following experimental datain Example 1.

EXAMPLE I Volume percent evaporation of gasoline after minutes inconstant temperature bath The above data show the advantages ofpropanepentane primed fuels and pentane primed fuels over butane primedfuel. In particular, the advantages of propane-pentane primed fuels overbutane primed fuels in regards to the percentage evaporated at 158 F.and the low vapor losses at both temperatures (135 F. and 150 -F.) aremost significant. As expected from FIGURE 2, the pentane primed fuel hasa low to normal vapor loss at the lower temperature but a much higherloss at the higher temperature. As known to those skilled in the art,typical losses between a refinery and an automobile engine are about 2to 4% on commercial butane primed gasoline, of which 12% are between therefinery and service station pump and the remainder represents filling,car tank, and carburetor vapor losses.

The effect of the gasoline priming agent on summer and winter typegasolines can be further demonstrated by the following data of ExampleII.

EXAMPLE II Effect of gasoline priming agent on car performance SUMMERGASOLINE 1 In a depentanized base gasoline. 2 Cars with poor chokingaction. a 1959 Ford data and assuming that the 158 F. point 13controlling The above data indicate the utility and advantages bothcommercial and practical to be obtained in cold starting 6 ability,initial warm-up ability, and in minimizing vapor losses at a constantVLTR when critical amounts hereinto before described, of propane in apropane-pentane primer are used to prime each type of gasoline, incomparison to the now prevalent commercial method of priming with butaneand butane-pentane mixtures.

EXAMPLE n1 To indicate the critical amount of propane in combina tionwith pentane that can be added to winter grade gasoline before theadvantage over the conventional C -C printing is lost, the followingdata are presented.

Win'ter gasoline (estimated values) Primer by volume Percent F. atPercent evap. 20% vapor RVP VLTR 3 at evap. loss at Percent PercentPercent 158 F. F 1

1 Estimated for standard evaporation test10 min. in bath at 115 F.

1 Measured value, also value of 1.3% was measured for gasolinecontaining about 50% pentane (VLTR of 18.1) and essentially no G; orCfs. From the above data, it can readily be seen that the actuallimitation on the propane in the propane-pentane priming of the wintergrade gasoline is about 4% byvolume of propane. The addition of morepropanepentane primer results in the advantage over the conventionalbutane-pentane priming of winter grade gasoline being lost.

EXAMPLE IV An improved gasoline of the instant invention can be preparedby the method of debutanizing a hydrocarbon base stock boiling in thegasoline boiling range in a conventional bubble column containing about30 trays. The column is operated at about 200 p.s.i.g. and has a toptemperature of about F. and a bottom temperature of about 330 F. Areflux ratio of about 0.5 to 0.8 is used. The reflux ratio is the ratioof the weight of liquid returned to the tower, to the weight of vaporproducts from the tower less the weight of liquid returned to the tower.The characteristics of the charge to the tower and the resultingproducts are given below:

The above debutanized gasoline is then primed with a mixture of apropane and a pentane fraction, so that the resultant product has about16.0 percent by volume of a pentane fraction and 1.6 percent by volumeof propane.

The above demonstrate the inventive method of priming a debutanizedgasoline with a propane-pentane mixture so as to minimize vapor loss ata constant vapor lock tendency rating.

In summary, the present discovery relates to the new concept of priminggasoline with pentane and up to a critical amount of propane, which isas much propane as possible, limited only so as to not exceed the Reidvapor pressure nor have less than the same percentage evaporated at 158F. nor a higher 20% point on a vapor basis than a butane primedgasoline. The propane-pentane or pentane primed gasoline will thenresult in a gasoline composition having superior starting ability,superior initial wa m lP and lower vapor and weathering losses than a.conventi nally primed gasoline of butane or butane-. pentane, ofsubstantially the same vapor lock tendency rating, It is apparent thatthe advantages of this invention, particularly in terms of theweathering and vapor losses can be obtained with all of the major typesof gasolines including automotive, marine type as well as aviationgasolines.

It will, of; course, be understood that the improved fuel composition ofthe present invention may also contain conventional amounts of othermaterials or additives, for example, various lead anti-knock compounds,such as tetraethyl lead and conventional lead scavenging agents of thetype well known to the prior art, as well as gum inhibitors, anti-icingagents, oxidation inhibitors, solvent oils and the like.

hat is claimed is:

1. A method of pressurizing a motor fuel to minimize vapor loss whilemaintaining a substantially constant vapor lock tendency rating, whichmethod comprises debutanizing a hydrocarbon base stock boiling in thegasoline boiling range, and priming said 'debutanized fuel with amixture of propane and pentane so that the total resultant compositionhas from about 1 to about 4% by volume of propane and a ratio by volumeof pentane to propane of between 5/ 1 and 50/ 1.

2. A method of pressurizing a motor fuel as defined in claim 1. whereinthe amount of propane comprises an amount of propane which will give apercentage evaporation at a vapor temperature of 158 F. and a vaportemperature at which 20% by volume evaporates of more than thatpercentage and less than that. temperature obtained when the said motorfuel is primed to the same vapor lock tendency rating with from 2 to 25%butane.

3. A method of pressnrizing a summer type motor fuel to minimize vaporloss While maintaining a substantially constant vapor lock tendencyrating which method comprises debutanizing a, hydrocarbon base stockboiling in the gasoline boiling range; and priming said debutanized fuelwith a mixture of propane and pentane, so that the total resultantcomposition has. from about 1 to about 2 percent by volume of propaneand a ratio by volume of pentane to propane of between 5/1 and 50/ 1 anda Reid vapor pressure of between about 7 and about 11 p,s.i.

4. A method of pressurizing a winter type motor fuel to minimize vaporloss while maintaining a substantially constant vapor lock tendencyrating which method comprises debutanizing a hydrocarbon base stockboiling in the gasoline boiling range; and priming said debutanized fuelwith a mixture of propane and pentane, so that the total resultantcomposition has from about 2 to about 4 percent by volume of propane anda ratio by volume of pentane to propane of between 5/1 and 50/ l and aReid vapor pressure of between about 12 and about References Cited inthe file of this patent The Science of Petroleum, Dunstan et al., OxfordUniversity Press, N.Y., 1938, pages 13921393.

The Chemical Technology of Petroleum, Gruse et al.,

McGraw-Hill Book Co. Inc N.Y., 1942, pages 455468.'

Oil and Gas Journal, vol. 29 (42), Mar. 5, 1931, Correlate VaporPressure and Losses by Lewis et al., pages 130, 220222.

1. A METHOD OF PRESSURIZING A MOTOR FUEL TO MINIMIZED VAPOR LOSS WHILEMAINTAINING A SUBSTANTIALLY CONSTANT VAPOR LOCK TENDENCY RATING, WHICHMETHOD COMPRISES DEBUTANIZING A HYDROCARBON BASE STOCK BOILING IN THEGASOLINE BOILING RANGE, AND PRIMING SAID DEBUTANIZED FUEL WITH A MIXTUREOF PROPANE AND PENTANE SO THAT THE TOTAL RESULTANT COMPOSITION HAS FORMABOUT 1 TO ABOUT 4% BY VOLUME OF PROPANE AND A RATIO BY VOLUME OFPENTANE TO PROPANE OF BETWEEN 5/1 AND 50/1.